Aging pushes an active and jubilant life into a sloth and sometimes miserably bed-ridden life. Aged adult's experiences age-associated diseases and loss of functionality. However, healthy aging is also observed within individuals who normally have active life throughout. An understanding of the underlying genetics of healthy aging may significantly improve human health. The essential question to this problem is (i) how tissues and organs age and (ii) what determines the lifespan? To elucidate the puzzle, specific response to molecular, environmental or genetic perturbation is observed throughout the lifespan of the animal. Utilizing the process, molecular biologists identified age-regulating signaling pathways such as insulin/insulin like growth factor (IGF-1), target of rapamycin, AMP kinase and signaling through sirtuins. These pathways alternatively are specific to their environmental and physiological stresses. In last two decades, more than hundred lifespan influencing genetic mutations have been discovered. These suggest, lifespan is a complex interaction of environmental factors and genetic. Hence, effect of any or combination of perturbation can be observed only through the lifespan of a population and lifespan study remains the core of aging research.
In addition, maintenance of muscle strength is essential for an individual's health and well being. In fact, loss of muscle strength is a prognostic indicator for a variety of disorders including sarcopenia, cancer, and neuromuscular diseases. Decline in muscle strength is also a significant issue for space explorers. Therefore, a major challenge for muscle health research is to understand the genetic mechanisms regulating strength.
Caenorhabditis elegans (C. elegans) is an established model organism for aging research. In addition, the C. elegans body wall muscles have similarities to the human muscle and also deteriorate with age much like in humans. Thus, prospective life-long muscle health studies can be accomplished in the roundworm C. elegans. It has a short lifespan of 3-5 weeks which allows observing the effects of genetic modification on the animal's lifespan in a relative short time period.
It is genetically tractable. Green fluorescent protein (GFP) tagging in the transparent body makes it ideal for observing age-related physiological and biochemical changes through the lifespan. Generally, C. elegans is cultured in bacteria lawn grown on agar plate and completes it's life cycle in 3 days. Predominantly, lifespan study is carried out on agar plate by manually transferring the adult worms periodically in new plates. Tedious agar plate based lifespan study severely limits the number of animals per experiment and number of experiments that can be carried out at a given time. This makes the timescale of a complete hypothesis test on the order of year. In addition to that, there are issues of loss of animal during study and contamination with bacteria/fungi. Variation in temperature, moisture/evaporation and quality of food contributes in lab-to-lab variation of lifespan. However, it is even more tedious and time intensive in case of any drug assay on lifespan due to the fact of diffusion limitation. Addition and withdrawal of drug/chemo-attractant has the same limitation of transferring the worms in new plates.
In agar plate, worms crawl by undulating their body sinusoidally in smooth surface. Generally, moisture from agar surface creates meniscus all along the body of the worm and capillary action actually pins the worm on agar surface. Worms have to continuously break the contact line and renew. Also, slips on the agar surface force the worm to work more. In its natural environment there are pores in the soil and some are connected. So, they feel the support of random size from all side of their body and can use the pores/walls of pores to support their crawling movement. It is likely that they will face lots of obstacles on their way as the pores have turns and dead ends. Naturally, head will forage a lot, touch sensory neurons will function constantly and muscles will be working all along the body for making the way out. It is now established that environmental stresses influence C. elegans lifespan to a considerable extent. In short, the environmental stresses in their natural environment are probably very different than in agar plate and probably result in underestimation of C. elegans lifespan.
A few attempts have been made recently to demonstrate liquid based lifespan devices. Most of them focused on reducing the manual intervention of transferring, prodding and scoring. A microfluidic chamber based device has been reported for the lifespan study in which worms were maintained in unobstructed circular chambers filled with liquid media and progeny was separated by inducing flow through a narrow channel allowing only the progeny to flow out of the chamber. The lifespan was reported to be 8-10 days at 24° C. for wild type animals based on 16 animals assay. A 96 well microtiter plate based lifespan study has also been reported in which the contamination with progeny was eliminated by using the drug 2′-deoxy-5-fluorouridine (Floxuridine, FUdR) to prevent hatching of eggs. Most recently, a microfluidic lifespan device (WormFarm) has been reported integrated with automated feeding and image analysis features in which a series of small channels connected to each side of the device was used as screen to separate progeny from the adult worms. A mean lifespan of 8.68 days (max lifespan 14 day) for wild type and 13 days (max lifespan 24 days) for age-1 was reported at 25° C. based on 200-400 animals. In all of the above techniques C. elegans are allowed to swim all through their life in their food environment. Worms maintaining swim gait throughout their life may experience stresses of unknown effect on their lifespan. It is also demonstrated that excessive swimming is detrimental for worm health. Use of drug FUdR reportedly has influence on C. elegans lifespan. Addition of valves in the microfluidic chip, requirement of pumps, interfaces for controlling fluid delivery to the device and software for image processing may limit a microfluidic lifespan device for easy, fast and bench-top use for a biologist. Around the same time, a capital intensive lifespan machine was reported which is a scanner based technology and can handle large population of worms in an experiment. A lifespan machine is capable of capture images and analyze lifespan automatically. However, it is still agar based assay and poses all the limitations of agar based lifespan scoring.